Mobilisation of cadmium by meso- and racemic-2,3-dimercaptosuccinic acid (DMSA) in rats

The role of chelation in the treatment of other metal poisonings

These proceedings will review the role of chelation in five metals-aluminum, cadmium, chromium, cobalt, and uranium-in order to illustrate various chelation concepts. The process of "chelation" can often be oversimplified, leading to incorrect assumptions and risking patient harm. For chelation to be effective, two critical assumptions must be fulfilled: the presumed "metal toxicity" must correlate with a given body or a particular compartment burden, and reducing this compartmental or the body burden (through chelation) attenuates toxicity. Fulfilling these assumptions requires an established dose-response relationship, a validated, reproducible means of toxicity assessment (clinical, biochemical, or radiographical), and an appropriate assessment mechanisms of body or compartment burden. While a metal might "technically" be capable of chelation (and readily demonstrable in urine or feces), this is an insufficient endpoint. Clinical relevance must be affirmed. Deferoxamine is an accepted chelator for appropriately documented aluminum toxicity. There is a very minimal treatment window in order to address chelation in cadmium toxicity. In acute toxicity, while no definitive chelation benefit is described, succimer (DMSA), diethylenetriaminepentaacetate (DTPA), and potentially ethylenediaminetetraacetic acid (EDTA) have been considered. In chronic toxicity, chelation is unsupported. There is little evidence to suggest that currently available chromium chelators are efficacious. Similarly, scant human evidence exists with which to provide recommendation for cobalt chelation. DTPA has been recommended for cobalt radionuclide chelation, although DMSA, EDTA, and N-acetylcysteine have also been suggested. DTPA is unsupported for uranium chelation. Sodium bicarbonate is currently recommended, although animal evidence is conflicting.

The effects of meso-2,3-dimercaptosuccinic acid and oligomeric procyanidins on acute lead neurotoxicity in rat hippocampus

Oxidative stress is considered to be a mechanism involved in lead neurotoxicity. Apoptosis is also thought to relate to lead neurotoxicity. The present study, focused on the hippocampus, was designed to investigate the two possible mechanisms involved in lead neurotoxicity and the potential protective effects of 2,3-dimercaptosuccinic acid (DMSA) and oligomeric procyanidins (OPC). It was proved that reactive oxygen species and oxidative damage were implicated in the induction of apoptosis induced by lead in the hippocampus. Administration of DMSA attenuated the oxidative stress and apoptosis in addition to having strong chelating and lead-removing capacity. OPC alone had antioxidant protective effects in the hippocampus but no removing capacity for lead in vivo despite showing higher affinity and stronger chelating ability for Pb(2+) than DMSA in vitro. It is suggested that OPC chelates Pb(2+) but does not discharge it from the body and even accumulates Pb(2+) in some organs. At the same time, a reasonable deduction can also be made that the complex of OPC-Pb(2+) prevents or at least weakens the neurotoxicity of Pb(2+). Whether this complex displays toxicity over a long time span should be studied further.

2,3-Dimercaptopropane-1-sulfonic acid and meso-2,3-dimercaptosuccinic acid increase mercury- and cadmium-induced inhibition of delta-aminolevulinate dehydratase

Compounds derived from Dimercaprol, such as meso-2,3-dimercaptosuccinic acid (DMSA) and 2,3-dimercaptopropane-1-sulfonic acid (DMPS), are becoming common agents for treating humans exposed to heavy metals. Heavy metals such as Pb(2+), Hg(2+) and Cd(2+) can inhibit delta-aminolevulinate dehydratase (delta-ALA-D) activity. Delta-ALA-D catalyzes the condensation of two delta-aminolevulinic acid (delta-ALA) molecules with the formation of porphobilinogen, a heme precursor. The effects of DMSA and DMPS alone or in combination with Cd(2+), Hg(2+), or Pb(2+) on hepatic delta-ALA-D were examined. DMPS and DMSA caused a dose-dependent inhibition of hepatic delta-ALA-D. In the presence of Hg(2+) or Cd(2+) the inhibitory potency of DMPS increased. Similarly, the inhibitory effects of Hg(2+) and Cd(2+) were markedly increased in the presence of DMSA. In contrast, the inhibitory effect of DMPS was not changed by inclusion of Pb(2+). As observed with DMSA, Zn(2+) did not modified the inhibitory effect of DMPS. Data of the present report support the idea that the complexes formed (metals-DMSA or DMPS) were more inhibitory than the metal (Hg(2+) and Cd(2+)) or the chelating agent alone to the hepatic delta-ALA-D activity, in vitro. The mechanism of hepatic delta-ALA-D inhibition by Hg(2+)-DMPS/DMSA and Cd(2+)-DMPS/DMSA complexes involve the essential thiol groups of the enzyme.